Water concentration control in phenol plant solvent



Sept. 1, 1970 R. P. OCONNOR WATER CONCENTRATION CONTROL IN PHENOL PLANT SOLVENT Filed Oct. 11. 1968 morzzomd A: m w OZFEEPm omwm 53 EEM R Inventor At torn ey United States Patent 3,526,587 WATER CONCENTRATION CONTROL IN PHENOL PLANT SOLVENT Richard P. OConnor, Flanders, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Oct. 11, 1968, Ser. No. 766,865 Int. Cl. Cg 21/16, 21/28 US. Cl. 208-321 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to solvent extraction of hydrocarbon fractions and especially to extraction of lubricating oil fractions with phenol. More particularly, this invention relates to recovery of phenol from the extract phase.

The use of phenol to extract aromatic hydrocarbons from lubricating oil feedstocks is well known. Parafiinic hydrocarbons make the best lubricants, and the presence of minor amounts of naphthenic hydrocarbons is acceptable. Aromatics have poorer lubricating properties than paraifinic hydrocarbons; they also reduce the viscosity index of the lubricant and have an adverse effect on color and stability. Hence it is common practice to extract aromatics from lubricating oil fractions, and phenol is widely used as the extractant.

The usual phenol extraction plant includes a treater tower in which a lubricating oil feed stock is countercurrently extracted with phenol, a raflinate fractionator tower, and an extract fractionation tower. A suitable hydrocarbon containing both parafiinic and aromatic hydrocarbons is introduced in the liquid phase into the treater tower. Liquid phenol is also introduced into the treater tower, where it countercurrently contacts the hydrocarbon. Aromatic hydrocarbons are preferentially dissolved in the phenol. Raflinate and extract phases are withdrawn separately. The rafiinate phase contains most of the paraffinic hydrocarbons, a substantial portion of any naphthenic hydrocarbons in the feed, and minor amounts of phenol. The rafiinate and extract phases are separately fractionated, and in each case the hydrocarbon is recovered as bottoms and the phenol as overhead. The raffinate bottoms consists primarily of parafiinic hydrocarbons suitable -for lubricants, usually after further refining to improve color and stability and to remove impurities such as sulfur. The phenol overhead is condensed and returned to the treater tower for re-use as an extractant. Phenol travels in a closed circuit with very low losses. Processes of the type described herein are illustrated in US. Pat. 2,923,680 to Bushnell, issued Feb. 2, 1960; US. Pat. 3,261,778, issued July 19, 1966; and in US. Pat. 3,274,096 to Bushnell, issued Sept. 20, 1966.

It is common practice to include a minor amount of water in the phenol extractant, since such minor amount improves both yield and selectivity of the extraction. Generally, the phenol extractant as it enters the tower contains about 2 to about by weight of Water. Nearly all of this water goes into the extract phase. The pre- 3,526,587 Patented Sept. 1, 1970 ferred amount of water depends on the composition of the feed stock, as well as on other factors such as the volume ratio of extractant to feed. The composition of the feed stock changes from time to time, and it is important to change the water percentage in the phenol extractant accordingly. The percentage of water desired in the phenol extractant in the treater tower is not always the same as the percentage of water in the phenol being recovered as overhead from the extract and rafiinate fractionation columns. Existing extraction systems either make no provision for varying the water content of the phenol or else they provide a still for fractionation of the phenol-water extract overhead. Since distillation is costly, it is desirable to find a more economical procedure to provide a phenol extractant of any desired water content within the operating range.

SUMMARY OF THE INVENTION According to this invention, an extract overhead consisting essentially of phenol and a minor amount of water is partially condensed to form a dry phenol condensate which contains less water than the amount desired in the phenol extractant. The uncondensed phenol and Water are condensed in a second stage to give a wet phenol condensate which has a greater percentage of water than that desired in the phenol extractant. The wet and dry phenol condensates are blended in proportions giving a phenol extractant of desired water content.

THE DRAWING The sole figure of the drawing is a flow sheet of the process of this invention.

DETAILED DESCRIPTION Referring now to the drawing, a hydrocarbon feed stock is countercurrently contacted with phenol containing a minor amount of water in treater tower 1 in order to remove aromatics therefrom. The hydrocarbon feed is introduced into treater tower 1 near the bottom through feed pipe 2, and the phenol is introduced into the top of treater tower 1 through inlet pipe 3. A raflinate phase containing parafiinic and naphthenic hydrocarbons plus a portion of the phenol extractant is removed overhead through line 4. An extract phase comprising phenol, water and the extracted aromatic hydrocarbons is removed from the bottom of the treater tower 1 through line 5. The extract phase contains most of the phenol introduced into treater tower 1.

In a preferred embodiment of the invention, the hydrocarbon feed stock introduced into treater tower 1 is a lubricating oil feed stock having a boiling point range of about 650 F. to about 1300 F., and containing desired parafiinic and naphthenic hydrocarbons plus undesirable aromatic hydrocarbons.

The pressure and temperature in treater tower 1, and the percentage of water in the phenol extractant introduced via inlet pipe 3 into tower 1, may follow conventional practices in the art. Typically, the pressure will be in the range of 50 to 300 p.s.i.g., and the percentage of water in the phenol extract will be in the range of about 2 to 15% by weight, preferably about 5 to about 10% by weight. The volume ratio of extractant to feed may be varied be tween about 50 to about 400 volumes of extractant per volumes of feed, preferably about 100 to about 200 volumes of extractant per 100 volumes of feed. This ratio is varied depending on the yield and selectivity desired. The conditions in treater tower 1 and especially the water content of the phenol may be varied depending on the nature of the feed stock and the desired yield and selectivity of separation. 'It is known that an increase in water percentage tends to improve both yield and selectivity.

Treater tower 1 may have plates or packing material such as Raschig rings in order to promote contact between the feed stock and the phenol extractant.

The rafiinate and the extract constitute two immiscible liquid phases which can be separated on the basis of difference in specific gravity. The raflinate, which is removed from tower 1 as the overhead phase via overhead line 4, consists primarily of paraflinic hydrocarbons, with naphthenic hydrocarbons if they are present in the feed, and only a minor percentage of phenol. Only a small por tion of the phenol extractant passes into the rafiinate phase, and the water content of the rafiinate phase is virtually nil. The raflinate is split into two streams 4a and 4b. The larger stream 4a, which accounts for most of the rafiinate phase, is heated in furnace 6 and is introduced into rafiinate tower 7 where it is fractionated. The smaller stream 4b by-passes furnace 6 and is introduced as a reflux liquid into the top of raffinate tower 7.

Rafiinate tower 7 is preferably a multiple plate column which may have a lower portion of greater diameter than the remainder of the column. This tower may be operated at pressures of about 40 to about 60 p.s.i.g. and temperatures of about 500 to about 800 F., preferably from about 50 to 55 p.s.i.g. and about 670 to about 700 F. A stripping gas, which may be nitrogen, air, or a lower molecular weight hydrocarbon or mixture of hydrocarbons (e.g., methane, natural gas, or a mixture of C -C hydrocarbons) is introduced into column 7 via gas inlet pipe 8a which is below raffinate inlet pipe 4. Nitrogen is a preferred stripping gas. The hydrocarbon content of the raffinate is recovered as bottoms via bottoms outlet 9. This hydrocarbon stream consists predominantly of parafiins with naphthenic hydrocarbons also present in those cases where they are present in the feed. This stream may be further treated, as for example by catalytic refining with added hydrogen, in order to improve color and stability. The raffinate bottoms stream, after such further treatment as is desired, is suitable as a lubricating oil base stock. The raffinate tower overhead is a gaseous mixture of phenol and stripping gas, which is removed from raflinate tower via overhead line 10. Thephenol is condensed as will be hereinafter described.

The extract phase is removed from treater tower 1 via line and is split into two streams 5a and 5b. The major stream 5a is heated in furnace 14, vaporizing most of the phenol and water content while leaving most of the oil content in the liquid phase. This stream 5a is introduced into extract tower 11 where it is fractionated into an overhead consisting predominantly of phenol and water and a bottoms consisting predominantly of hydrocarbons. The minor stream 5b by-passes furnace 14 and is introduced as a reflux liquid stream into the top of extract tower 11. A stripping gas, preferably of the same composition as the stripping gas entering raffinate tower 7 via line 8a, is introduced into the bottom of extract tower 11 via line 8b. The extract tower is operated at a pressure of about 40 to about 60 p.s.i.g. and a temperature of about 500 to about 800 F., preferably about 50 to 55 p.s.i.g. and about 575 to 625 F. The bottoms product, removed through line 15, consists essentially of aromatic hydrocarbons with no more than traces of phenol and water. Virtually all the phenol and water in the extract phase are recovered overhead in overhead line 16.

The extract tower overhead is treated by a novel process according to this invention in order to produce a reservoir of dry phenol and a separate reservoir of wet phenols without distillation. The contents of these two streams can then be mixed in proportions which will give a phenol extractant of desired water content for use in treater tower 1.

The extract tower overhead 16 is cooled and reduced in pressure from the levels prevailing at the top of extract tower 11 to the levels required for forming a condensate of substantially pure phenol While maintaining virtually all of the water in the vapor phase. This is accomplished by indirect heat exchange with the incoming extract in heat exchanger 13, with additional cooling and pressure reduction as required. The phenol condensate is collected in dry phenol drum 17. This drum is typically operated at a pressure of about 25 to 35 p.s.i.g., and a temperature of about 350 to 380 F. The temperature is somewhat higher than the temperatures prevailing in the phenol drums in prior art systems. The phenol collected in dry phenol drum 17 may have a small Water content, usually only about 0.1-4% by weight, but in no case can the water content exceed the minimum water content desired in the extractant used in treater tower 1. Water vapor and uncondensed phenol are removed from dry phenol drum 17 via line 18, and are cooled in heat exchanger 12 and in condenser 19 to condense both phenol and water. The condensate is collected in wet phenol drum 20. The wet phenol collected in drum 20 will usually contain about 16 to 70% by weight of water, and the water content of the wet phenol is always greater than the water content of the phenol extractant in treater tower 1. The temperature in wet phenol drum is about to F., which is much lower than in dry phenol drum 17, but the pressure is only slightly lower, i.e., in the range of about 20 to 30 p.s.1.g.

In a typical operation according to this invention, substantially pure phenol containing about 0.15% by weight (about 0.16% by volume) of water is collected in drum 17, and wet phenol containing about 15.6% by weight (about 16.5% by volume) of water was collected in drum 20. In this same typical operation, streams 21 of dry phenol and 22 of wet phenol are withdrawn from drums 17 and 20, respectively, and mixed in proportions giving an aqueous phenol extractant containing 4.95% by weight (5.3% by volume) of water.

The raffinate tower overhead consisting of phenol vapor and stripping gas is mixed with the uncondensed gases and vapors from dry phenol drum 17. Admixture preferably takes place upstream of heat exchanger 12. The quantity of phenol in the raffinate overhead is usually very small compared to the quantity of phenol in the extract overhead. The stripping gas is not condensed in condenser 19, and is removed from wet phenol drum 20 via line 8. The stripping gas in line 8 generally contains small amounts of phenol and water vapor, and these may be removed by known means such as a knockout drum not shown. After water and phenol are removed, the stripping gas in line 8 is split into two streams 8a and 8b leading to raffinate tower 7 and to extract tower 11, respectively.

Dry phenol and wet phenol are withdrawn from their respective drums 17 and 20 in proportions which will give a phenol extractant of desired water content for introduction into treater tower 1. Withdrawal from drums 17 and 20 takes place through withdrawal lines 21 and 22, respectively. These lines have pumps 23 and 24, respectively, for pumping phenol up to the pressure in treater tower 1. Dry phenol is cooled in cooler 25 where necessary prior to admixture with wet phenol. The two phenol streams are mixed in mixer conduit 26, which is connected to treater tower inlet pipe 3'.

It will be observed that the phenol travels in a closed system. Most of the phenol travels from treating tower 1 to extract tower 11 via line 5, then to drums 17 and 20 via line 16, and from drums 17 and 20 back to treater tower 1 via mixer conduit 26 and inlet 3. A portion of the phenol, usually about 2' to 8% of the total, travels from treater tower 1 to rafiinate tower 7 via line 4, and is returned to wet phenol drum 20 via raflinate overhead line 10. The circuit from phenol drum 20 back to treater tower 1 is the same as described above. Losses from the closed phenol system are quite small.

This invention will now be described in further detail with reference to the following examples, which illustrate specific embodiments of the invention.

EXAMPLE 1 This example illustrates the separation of aromatics from a vacuum shell still distillate obtained from Kuwait crude using the process of this invention. The distillate has the following properties:

Boiling point range, F 895-1020 Viscosity, SSU at 100 F 1455 Viscosity, SSU at 210 F. 87.0 Viscosity index 50 Gravity, API 18.6

The process follows the flow sheet shown in the sole figure of the drawing. All liquid volumes are based on 100 volumes of feed, and all gas volumes are expressed in standard cubic feet per barrel of feed (s.c.f./b.).

One hundred parts by volume of feed per hour, and 180 parts by volume by hour of extractant, are introduced into treater tower 1 via feed stream line 2 and extractant stream line 3, respectively. The treater tower 1 is operated at a temperature of 172 to 182 F. and at a pressure of 237 to 257 p.s.i.g. The extractant contains 94.7% by volume phenol and 5.3% by volume water. A rafiinate 4 having a flow rate of 54.4 volumes per 100 volumes of feed and a composition of 82.5% by volume of oil phase and 17.5% by volume of phenol, is removed from the treater tower 1 as the overhead product. The extract 5, which is removed as the bottoms product of treater tower 1, has a flow rate of 206 volumes per 100 volumes of feed, and has a composition of 24.4% by volume oil, 71.4% by volume phenol, and 4.2% by volume water. The rafiinate and extract are separately fractionated in rafiinate tower 7 and extract tower 11 respectively; the raflinate tower is operated at an average temperature of 570 F. and a pressure of 50 to 55 p.s.i.g., while the extract tower is operated in an average temperature of about 520 F. and at a pressure of 50 to 55 p.s.i.g. The raflinate bottoms 9 is an oil phase consisting essentially of paraffinic and naphthenic hydrocarbons, with small amounts of dissolved nitrogen but with no phenol or water. The extract bottoms 15 is an oil phase, free of phenol and water, which consists predominantly of aromatic hydrocarbons. The extract overhead 16, containing 92.0% by weight of phenol, 5.1% by weight of water, and 2.9% by weight of nitrogen stripping gas (on a volume or mole basis, the composition is 71.6% by volume phenol, 20.8% by volume water and 7.6% by volume nitrogen), is conveyed to the dry phenol drum 17, where partial condensation takes place, producing a dry phenol condensate containing 99.8% by volume phenol and 0.2% by weight water. The dry phenol drum is operated at 370 F. and 30 p.s.i.g. The uncondensed gases from the dry phenol drum are mixed with the raffinate overhead 10, and the phenol and water contents of the combined gas streams are condensed in wet phenol drum 21, which is operated at 105 F. and 28 p.s.i.g. The wet phenol condensate contains 83.5% by volume phenol and 16.5% by volume water. The stripping gas remains uncondensed and is removed via line 8. Dry phenol and wet phenol are removed from their respective drums in the proportions required to give the extractant 3 of the designated composition.

EXAMPLE 2 Aromatics are extracted according to this example from a vacuum shell still distillate of a Tia Juana crude. The distillate has the following properties:

Total boiling point range, F 650-790 Viscosity, SSU at 100 F 128 Viscosity, SSU at 210 F. 39.8 Viscosity index 25 Gravity, API 23.2

The extraction process illustrated in this example also follows the flow sheet in the sole figure of the drawing.

Nitrogen is used as the stripping gas. The feed in this example has a somewhat lower viscosity index than the feed in Example 1, indicating a higher aromatics content. This example illustrates a substantially lower ratio of extractant to feeds than that used in Example 1.

According to this example, parts by volume per hour of feed 2 and 100 parts by volume per hour of extractant 3 are introduced into treater tower 1, which is operated at an average temperature of about 135 F. and an average pressure of about 247 p.s.i.g. The raffinate 4 has a flow rate of 72 volumes per hour and a composition of 97.2% oil and 2.8% phenol per volume. The extract 5 has a flow rate of 128 volumes per hour and a composition of 23.5% by volume of oil, 66.4% by volume of phenol, and 10.1% by volume of water. The raffinate is fractionated in rafiinate tower 7, operated at an average temperature of about 560 F. and a pressure of about 50 to 55 p.s.i.g., yielding a bottoms 9 consisting essentially of parafiinic and naphthenic hydrocarbons having a flow rate of 70.3 volumes per hour. The raffinate overhead consists essentially of phenol, water and nitrogen with substantially no hydrocarbons. The extract is fractionated in extract tower 11, operated at an average temperature of about 510 F. and a pressure of about 50 to 55 p.s.i.g., to yield 30.1 volumes per hour of a bottoms consisting almost entirely of hydrocarbons (except for small amounts of dissolved nitrogen) and comprising predominantly aromatic hydrocarbons, and an overhead of phenol, water and nitrogen which is essentially free of hydrocarbons. The extract overhead 16 has a composition of 84.4% by weight phenol, 12.0% by Weight water, and 3.6% by weight nitrogen (52.9% by volume phenol, 39.5% by volume water, and 7.6% by volume nitrogen). This extract overhead is partially condensed to yield a dry phenol condensate containing 95.5% by volume phenol and 4.5% by volume water. This condensate is collected in dry phenol drum 17, which is operated at a pressure of 30 p.s.i.g. and a temperature of 350 F. The uncondensed gases are mixed with the raflinate overhead and the resulting gas mixture (except for its nitrogen content) is condensed in wet phenol drum 20, yielding a condensate containing 38.8% phenol and 61.2% water by volume. The wet phenol drum is operated at 28 p.s.i.g. and F. The dry phenol and Wet phenol condensates are mixed in the proportions which will give an extractant 3 of the previously specified composition.

It will be recognized that details in the foregoing specification and examples are by way of illustration and not limitation.

What is claimed is:

1. A process for selective extraction of aromatics from a hydrocarbon feed stock with phenol which comprises contacting the feed stock with a phenol extractant containing a minor amount of water, separately recovering an extract phase and a rafiinate phase, fractionating said extract phase to obtain an extract overhead comprising phenol and a minor amount of water and an extract bottoms comprising aromatic hydrocarbons, partially condensing the extract overhead under conditions of elevated pressure and temperature to form a substantially dry phenol condensate containing a lower percentage of water than the aforesaid phenol extractant and an uncondensed vapor phase having a greater percentage of water than said phenol extractant, condensing said vapor phase to form a wet phenol condensate and blending said dry phenol condensate and said wet phenol condensate to form said phenol extractant having a predetermined water content.

2. A process according to claim 1 in which said raflinate phase is fractionated separately from said extract phase to produce a bottoms containing non-aromatic hydrocarbons and an overhead containing phenol, and mixing said phenol with phenol vapor obtained as extract overhead.

3. A process according to claim 2 in which said mixing takes place after said dry phenol condensateis formed.

7 8 4. A process according to claim 1 in which said hydro- 2,846,354 8/1958 Holm et a1. 208335 carbon feed stock is a lubricating oil feed stock contain- 2,923,680 2/ 1960 Bushnell 208321 ing paraffimic and aromatic hydrocarbons. 3,329,606 7/1967 Miller et a1 208335 References Cited r HERBERT LEVINE, Primary Examiner 0 UNITED STATES PATENTS Us CL 2,216,933 10/1940 Atkins 208*335 208-324, 335

2,673,174 3/1954 King 208-321 

